I have had tachycardia since 2003, not pinpointed why,but when I go to sleep ,a sharp pain shoots thru my high chest wakes me up and a panic attack starts. stress test says heart is good ,left atrium dialated ,good study,on metoprolol 25mg twice daily but no one gives an answer.I have thyroid problem and I take synthroid 25 mcg daily,but no reason for tachycardia.